How make automatic spell that transforms enemy unit to another unit?

[WC3Wonderer]

1. I have 10 sourceress on the screen. This sourceress attacks enemy bease.
2. I have 10 sourceress outside of the screen. This sourceress defends my base.
3. My sourceress can Polymorph two Level 2 enemies into sheep.
4. In total I have 20 sourceress in different places on the map.
5. I can't controll 20 sourceress with two hands.

I need more hands or cast polymorph automatically. How make automatic spell that transforms enemy unit to another unit?

 

[Bender]

• Remove Polymorph from the Sorceress.
• Create a copy of Polymorph that does not cost mana nor any upgrades and has a long cooldown.
• Create a copy of Curse (or another offensive autocast spell) and give it to the Sorceress.
• Set this Curse it up so it does nothing, and that it's buff lasts for 0.01 seconds.
• Create a trigger that detects when Curse is cast, so that it creates a dummy that casts the custom Polymorph on the Curse target.
• Give the dummy a short expiration timer.